Visibility ON/OFF in the BGE via Python
You can do:

own['trails'] = trailsObject
own['trails'].visible = True
own['trails'].visible = False


or as i can see in the image:

cont.activate(trails) # to activate the actuator
cont.deactivate(trails) # to deactivate the actuator


Also visit the BGE Documentation.

Next time please take a moment to copy your code as text and format it.